1. Field of the Invention
The present invention relates to a functional roll film and a vacuum evaporation apparatus capable of producing the functional roll film, and more particularly, to a functional roll film having excellent characteristics as a packaging material requiring hermeticity for a food product, a medical product, electronic parts and the like having excellent transparency, gas barrier properties, printing properties, flexibility and the like, or as a gas shut-out material, and the invention also relates to vacuum evaporation apparatus capable of producing such a functional roll film.
2. Description of the Related Art
A functional roll film such as a transparent gas barrier film comprises an inorganic matter laminated on a plastic film which is a base material. As the inorganic matter, a metal oxide is widely utilized for enhancing transparency. As the metal oxide, films on which silicon oxide, aluminum oxide, magnesium oxide or a mixture of these elements is laminated by a vacuum evaporation method using a vacuum evaporation apparatus or a CVD method using a CVD apparatus are commercially available. The produced transparent gas barrier film is cut into pieces by a slitter, each having a width of about 400 to 1,000 mm and a length of about 4,000 to 10,000 m, and each pieces is wound around a paper core and is put into circulation in a form of a film roll. Converter makers laminate another film or paper on the take-up film, or print the wound film onto a transparent gas barrier film and then, further laminate another film thereon, and produce various packaging laminated films.
Naturally, performance of the transparent gas barrier film largely depends on the thickness of its inorganic thin film layer. Barrier performance of the transparent gas barrier film that a thin film layer is laminated on the plastic film has a tendency that gas permeability is reduced as the thickness of the thin film layer is increased from a state in which nothing is laminated. However, if the thickness of the thin film exceeds a certain film thickness, the reduction effect of gas permeability is not enhanced as compared with the increase in the film thickness. On the contrary, if the thickness is excessively increased, the flexibility of the thin film is lowered, and the thin film layer is prone to be broken, and there is a problem that the gas barrier performance is lowered. Therefore, it is preferable that the thin film layer is formed with a minimum thickness in which the gas barrier properties are stable.
On the other hand, when the transparent gas barrier film is produced, the thickness of the thin film layer must be controlled, but under present circumstances, an optical monitor used for measuring the thickness of the thin film does not have excellent precision of film thickness measurement in generally. The thickness of the thin film is measured by illuminating a plastic film on which a thin film layer is laminated from one side of the film, receiving the transmitted light from the other side, and calculating the thickness of the thin film by the intensity of the light. However, the thin film layer of the transparent gas barrier film has excellent light transmission properties, a variation in the light transmission amount is small as compared with a variation in film thickness and therefore, the measurement precision is not excellent.
On the other hand, if a degree of oxidation of silicon oxide or aluminum oxide is varied, the thin film layer is colored and the light transmissivity is varied. Thereupon, in order to avoid such an influence, light having a specific wavelength is used. However, it is still difficult to measure the thickness of the thin film with sufficient precision.
Conventionally, since the thickness of the thin film is measured using such an optical monitor of low precision, even if an attempt is made to control the thickness of the thin film based on the measured result of the monitor, it is impossible to stable the thickness of the thin film within a preferable range.
Thereupon, in order to secure the gas barrier properties in the entire region of the film, an attempt has been made to produce the film such that the minimum thickness of the thin film among the width variation of thickness becomes a thickness which stabilizes the gas barrier properties.
However, since the measuring precision of the thickness of the thin film itself is not excellent, the variation in thickness of the thin film is inevitably increased, and especially when the laminated inorganic matter layer is composite oxide, it is extremely difficult to precisely measure its component and therefore, it becomes more difficult to suppress the variation in thickness of the thin film. Therefore, with the conventional apparatus, it is difficult to obtain a transparent gas barrier film roll having stable thickness and composition of the thin film and stable gas barrier properties.